Incinerator kilns, and especially those of the rotary type, have an outside metallic shell, usually steel, the inside of which is fully covered by a thick ceramic or refractory, usually in the form of fire bricks having a total thickness exceeding in many cases 25 cm. These kilns usually operate at a exit gas or off-gas temperature in the range of about 1,600.degree. to 2,400.degree. F. The ceramic or refractory walls, however, are very vulnerable to erosion and corrosion, due to the hostile conditions created by the nature of incinerated materials and high temperatures, especially, if alkali metals are present.
If the viscosity of slag in the kiln is adequately high, it may form a rather thick viscous coating on the refractory and thus protect it from the hostile environment. However, when the viscosity of the slag is very low, the slag contributes to the erosion and corrosion of the ceramic, both chemically because it serves as a solvent and mechanically, as it allows foreign big pieces of abrasive material to act against the ceramic walls. If the slag is viscous to the point of becoming substantially solid, or if it has never been formed as a liquid, it becomes ineffective in promoting combustion of organic matter, and also in capturing toxic heavy metals. Therefore, it is imperative that the viscosity of the slag is very carefully monitored and controlled within a range of values. Thus, one of the objects of this invention is to control the viscosity of the slag in incinerating kilns.
U.S. Pat. No. 5,301,621 (Vassiliou et al.), which is incorporated herein by reference, describes methods and devices for slag viscosity detection through image analysis of dripping slag within rotary incineration kilns.
U.S. Pat. No. 5,228,398 (Byerly et al.), which is also incorporated herein by reference, describes methods and devices for controlling rotary incineration kilns by determining the position of the kiln outlet at which the slag is exiting.
U.S. Pat. No. 5,353,722 (Vassiliou et al.), which is also incorporated herein by reference, describes preventive slag-viscosity control by detection of alkali metals in the off-gases.
U.S. Pat. No. 4,953,481 (Clayton) discloses the use of melting point enhancers to control slag build-up in garbage, medical waste and sludge incinerators. It is directed to method of modifying the nature of low melting non-combustible components of garbage, medical waste and sludge by the addition of very high melting point metallic compounds so as to render the low melting point materials non adherent or less adherent and easier to remove from furnace surfaces.
U.S. Pat. No. 4,846,083 (Serbent) discloses the production of a product which can be dumped or utilized. The mineral are subjected to a thermal treatment in a rotary kiln, at a temperature at which the charge of the rotary kiln is transformed to a pasty or liquid slag phase. The composition of the charge is so selected that a slag phase is produced in which the main components, which constitute a matrix, are in the range from 60 to 72% SiO.sub.2, 10 to 30% Al.sub.2 O.sub.3, and 5 to 25% CaO+MgO, of said matrix, wherein the total percentage of SiO.sub.2 +Al.sub.2 O.sub.3 +CaO+MgO equals 100, the total of the main components SiO.sub.2, Al.sub.2 O.sub.3, CaO, and MgO amounts to more than 60% on dry and ignition loss-free basis, of the mineral matter which is charged to the rotary kiln. The slag Phase discharged from the rotary kiln is cooled and the exhaust gas from the rotary kiln is purified.
U.S. Pat. No. 4,473,379 (Liu) discloses improvement of the performance of a slagging coal gasifier by injecting finely divided particles of non-corrosive slag-like solid material into the gasifier near the zone of combustion at a rate at which heat-protective layers of solidified slag are maintained between that zone and metallic materials located near that zone.
U.S. Pat. No. 4,253,408 (Kramer) discloses a method of preventing corrosion of incinerators designed to burn sewage consisting essentially of from about 90 to 98 percent water and from about 2 to 10 percent waste solids by increasing the fusion temperature range of the ash product above the operating temperature of the interior surfaces of the incinerator. The sewage is mixed with additive materials selected from the group SiO.sub.2, CaO, Al.sub.2 O.sub.3, and MgO wherein the CaO, Al.sub.2 O.sub.3, and MgO are selected from within the range of 10 to 30 percent of the weight of the waste solid sand the SiO.sub.2 is selected from within the range of 25 to 30 percent of the weight of the waste solids. Thereafter, the sewage additive mixtures are injected or otherwise dispersed into the combustion zone of an incinerator such that the waste solids and additive particles remain in contact therein for sufficient time for the additives to chemically combine with sewage solids and form combustion products having fusion temperatures ranges above the operating temperatures of the incinerator surfaces.
U.S. Pat. No. 3,340,393 (Landes et al.) discloses a machine with lining bricks which have a face exposed to wear and side and end surfaces which equal the thickness of the bricks and are concealed by adjacent bricks, said thickness defining surfaces having applied thereto wear indicating means. Said means comprise a right angle triangular design in which one of the right angle edges is perpendicular to the exposed face of the brick and located at a distance from the adjacent parallel edge of the thickness defining surface to which the design is applied, the other of its right angle side edges being coincident with and visible at the exposed face of the brick, both said side edges being equal in length to the thickness of the brick. The length of the visible edge of the triangular design changes progressively as the exposed face becomes worn and at all times equals the thickness of the brick.
U.S. Pat. No. 2,289,877 (Davis) discloses refractory lining for rotary kilns, and refractory members useful for forming such lining, as well as processes for making the same.